The present invention relates to a golf club head, and more particularly to a method for manufacturing a golf club head capable of adjusting the coefficient of restitution of the titanium face easily without degrading other performances.
In recent years, with the progress of manufacturing technology and the like, various golf club heads having large coefficient of restitution and large moment of inertia have been proposed, for instance, as disclosed in JP-A-8-280853. Thus, the increase in ball carry distance in recent years is very notable. Therefore, concerned about such a tendency to increase carry distances leaning on the manufacturing technologies, golf associations, e.g. “U.S.G.A.”, “R & A” and the like have established a rule that controls the coefficient of restitution*1 of golf club heads to a certain value (less than 0.830). Actually, most of wood-type hollow titanium face club heads put on the market at present have a coefficient of restitution of 0.830 or more. Therefore, in order to make golf clubs usable in official competitions, it is needed to use a club head having a coefficient of restitution smaller than those of conventional club heads so as to meet the above-mentioned regulated value for the coefficient of restitution. (*1: measured according to the U.S.G.A Procedure for Measuring the velocity Ratio of a Club Head for conformance to Rule 4-1e, Revision 2, Feb. 8, 1999)
An effective method for decreasing the coefficient of restitution is to increase the rigidity of the face portion of club heads by increasing the thickness thereof. If however the face portion is increased in the thickness, as the weight of the face portion increases, the center of gravity of the head shifts toward the club face and the depth thereof becomes shallow. In the case of a hollow titanium alloy head for driver having a volume of 400 cc and a face surface area of 40 sq.cm, if the thickness of the face portion is increased by 0.5 mm, the weight of the head increases by 5 grams in the face portion. Accordingly, a significant amount of shift of the center of gravity toward the face is unavoidable. As well known, a club head having a shallow depth of the center of gravity has a poor directional stability with respect to shot directions since the amount of movement of the head at miss shot becomes large, but rather the increase in the weight impose restraints on the design freedom for the head especially the center of gravity.